This could be a number of things. I have not personally had that happen, although it could be a low air and water temperature, make sure both mediums are heated, with the water being slightly warmer than the air. Although if it still is young you wouldn't have a mating call, but babies call to make their mother aware, perhaps this habit was never broken, depending on how you treated the gator it could be a call for you or a friendly figure. Another and most severe of the three is a respiratory infection, an excess of mucus and flem in the throat and lungs can cause them to "sneeze" to try and get it out like they do with water when they emerge. I recommend you test these reasons. See if your company makes him stop. Or try heating up his temps, remember this is a Floridian reptile. Good luck